Some completions involve long runs of screens in the producing zone. To get more balanced production along a lengthy section of screen that in some cases could be thousands of feet long devices have been used to offer different resistance at different locations along the screen sections. The screen sections closest to the surface that constitute a potential path of least resistance would need more restriction that screen sections further down. What has been tried in the past is illustrated in U.S. Pat. No. 6,622,794. In this patent screen sections had an annular space between a base pipe and the screen and inserted in the annular space before the flow could get to openings in the base pipe were helical paths that offered different degrees of resistance to a given flow rate. Using this design would require expensive machining raising the cost of each stand of screen. Additionally, an inventory of different screens opening sizes had to be kept and for each screen opening size the spiral paths that created different levels of resistance to a given flow also had to be kept in inventory for a variety of different completion situations. Beyond that, the screen sections needed to be carefully marked so that they would be assembled at the well in the correct order so as to provide more flow resistance closer to the wellhead and tapering down to less of no resistance at locations most remote from the wellhead.
Apart from this design sliding sleeves have been run with screens and some examples of those designs are U.S. Pat. Nos. 5,896,928; 6,371,210; 7,096,945; 7,055,598; 6,994,170; 6,481,494; 6,978,840; 6,568,472 and US Publication No. 2006/0237197.
The present invention provides an economical design for balancing screen flow particularly well suited for applications where highly viscous hydrocarbons about 10 to 10,000 centipoise with a preferred range of 20-1000 centipoise are being produced. In these situations the screen design incorporated an annular flow path to the base pipe openings that can be high enough to pass solids that might clear a screen and yet provide enough flow resistance at high viscosities to achieve the desired screen flow balancing. The design is considerably cheaper to produce than the prior spiral path designs. These and other benefits of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the claims are the full measure of the invention.